These electronic circuits are used for radar type applications in which an electromagnetic wave is sent at a millimetric frequency and a wave reflected by an obstacle is received by an antenna, to extract from this wave, on the one hand, distance information and, on the other hand, relative speed information, between this obstacle and the source that sent the wave.
The millimetric frequency circuits can also be used for short distance and very high bit rate communication applications.
Whatever the application, the electronic processing of the millimetric frequency signals comprises a low frequency processing part that can be implemented by silicon integrated circuits mounted on printed circuits. This part can be produced by very commonly used and inexpensive technologies, with connections that are simple to produce between circuit elements on one and the same integrated circuit chip or between different integrated circuit chips. The processing also comprises a very high frequency part (greater than 45 GHz), that can be implemented only by components and integrated circuits made of semiconductor materials other than silicon (gallium arsenide GaAs and its derivatives in particular, or even SiGe). These integrated circuits are called “microwave monolithic integrated circuits” or MMIC. This high-frequency part raises problems of production that are difficult and usually prove very expensive.
In practice, for relatively complex functions, it is necessary to use a large number of MMIC integrated circuit chips, since the quantity of circuit elements that can be placed in one and the same chip is far more limited for the MMIC circuits than for the low frequency circuits made of silicon. Also, these chips are mounted on a substrate with interconnections that are difficult to produce given the very high working frequencies. The design of the interconnections is difficult, and the production cost is high because of the precision required in maintaining tight tolerances to ensure the transmission of the millimetric frequency signals. This becomes all the more true as the number of MMIC chips increases in the system. Also, the increase in complexity of the functions that are to be produced brings with it an increase in the number of chips.
Mounting the chips on a hybrid substrate (normally mounting with wiring to link the chips to the hybrid substrate) is itself very expensive when the number of chips is high.